1. Field of the Invention
This invention relates, in general, to an energy absorption apparatus and, specifically, to apparatus for controlling the rate of movement of two telescoping members with respect to each other. More specifically, the present invention relates to a vehicle steering shaft assembly which collapses upon impact imposed by a human body on the steering shaft assembly.
2. Description of the Prior Art
During the collision of a motor vehicle, such as an automobile or truck, with another object, the driver is typically thrust forward into the steering wheel. Due to the rigidity of the steering wheel and supporting column, extreme forces are exerted on the driver's body which could cause severe if not fatal injuries to the driver.
As a result, numerous attempts have been made to devise a steering column which collapses when a pre-determined amount of force is exerted on the column so as to minimize the force exerted on the driver during a collision. Current steering wheel columns manufactured for motor vehicles are typically formed of two slidable sections which telescope upon impact of the driver with the steering wheel. Various elements and components have been added to the steering column to control the rate of telescoping of the first and second shafts. Most of these previously devised collapsible steering columns structures include elements or components which deform or are separated when a pre-determined force level caused by impact of the driver on the steering wheel and steering column.
Once such attempt is shown in U.S. Pat. No. 3,703,106 which discloses a steering column assembly including a combination support and guide member. The combination support and guide member is rigidly attached to the body remote from the instrument panel. The guide member includes a channel of increasing depth which receives a pair of lugs mounted on a bracket attached to the steering column. During collapse of the steering column, the lugs are progressively more tightly wedged into the combination support member to provide supplementary energy absorption.
In the collapsible steering column disclosed in this last mentioned patent, the combination support and guide member is mounted exteriorally on the steering column and interacts with lugs formed on the column structure itself. This imparts all forces during collapse on the column thereby requiring a large column structure.
The internal interconnected and rotatable shafts of the steering assembly must also telescope. Such shafts are typically secured together for rotation by means of clips and fasteners to provide the desired simultaneous rotation of both shafts, as well as to eliminate lash which causes rattle during movement of the vehicle.
However, such currently devised clips include metallic springs which hold both of the telescoping shaft members together for rotation and yet allow a collapse or telescoping of the upper member attached to the steering wheel within the lower fixed shaft member. These spring devices have a generally low fatigue life which, over increased driving miles, causes wear on the clips and therefore lash in the steering column between the two shaft members. This affects steering of the vehicle thereby leading to more difficult control of the vehicle causing driver fatigue from overcorrecting the steering or rattling noise in the steering column.
Plastic inserts or clips have also been used to connect the two telescoping shaft members together. However, such plastic inserts have a low breakaway characteristic followed by a zero collapse rate. Such plastic clips are also subject to premature shearing which again results in the above-listed problems.
The uncontrolled collapse of the steering column leads to problems during a so-called "second collision" or impact of the driver with the steering column. The typical collapsible steering column begins to collapse when a pre-determined force, such as a certain amount of impact of the driver on the steering wheel itself is placed on the steering column. This causes separation or rupture of the steering column assembly and the resultant collapse of the steering column. Such collapse, however, is uncontrolled, that is, it proceeds at a rate dependent upon the amount of input force until the steering column bottoms out.
In view of the uncontrolled rate of collapse of previously devised collapsible steering columns, it would be desirable to provide an energy absorption apparatus which would provide a controlled rate of collapse of the apparatus. It would also be desirable to provide an energy absorption apparatus which finds particular advantageous use in a collapsible steering column and which provides a controlled movement of the telescoping steering shaft members during collapse of the steering column. It would also be desirable to provide an energy absorption device which is easily assembled without requiring additional, specially designed brackets, sleeves, and other components for mounting the device on a conventional steering column. It would also be desirable to provide an energy absorption apparatus which is usuable in various applications without requiring extensive modification to existing components. It would be desirable to provide an energy absorption apparatus which can be assembled without the need for additional clips or fasteners to connect the rotatable members of the absorption apparatus and prevent lash between the various components. It would also be desirable to provide an energy absorption apparatus which can be taken apart and re-assembled many times without any effects on the operability of the apparatus. Finally, it would be desirable to provide an energy absorption apparatus which can be formed with any desired energy absorption rate dependent upon the particular application to which it is applied.